System, apparatus and method for detecting wireline tools

ABSTRACT

The present disclosure provides a system, an apparatus and a method for detecting line-attached tools in an above-surface portion of a well for use during well-work overs and/or interventions. The system includes the apparatus which comprises: a body for housing at least one magnetic-field generator and at least one magnetic-field sensor; and a tubular portion that is configured to be housed within the body. The tubular portion has a bore for receiving the line-attached tools and the at least one magnetic-field sensor is configured for detecting changes in the magnetic field caused by the line-attached tool approaching, moving through and/or moving away from the body. The system may further include a processor unit for receiving one or more signals from the at least one magnetic-field sensor and for determining the location and/or one or more dimensions of the line-attached tool while approaching, moving through or moving away from the body.

TECHNICAL FIELD

This disclosure generally relates to oil and gas well work-overs andinterventions. In particular, this disclosure relates to a system, anapparatus and a method for detecting line-attached tools in anabove-surface portion of a well for use during well-work overs and/orinterventions.

BACKGROUND

Lines, such as wires and cables, are used in the oil and gas industry toperform well-work overs and/or interventions. There are two generaltypes of lines that are referred to as slickline or wireline. Slicklineis a wire or cable that can be used to insert a tool into a well toplace, adjust or retrieve well components. Wireline is typically a cablethat is also used to insert a tool into a well. Typically, wirelineincludes at least one electrical conductor that conducts electricalpower and data to and from the tool. Wireline is often also used in welllogging.

A typical approach for retrieving a line-attached tool involves pullingthe line out of the well with a hydraulically powered reel upon a linetruck until almost all of the line is retrieved. Then the line is givensome slack and a user pulls on the line at a point between the top ofthe wellhead lubricator and the line truck. Then the line is pulledslowly until the user identifies tension in the line. The tension ispresumed to be caused by the tool contacting the uppermost pack-off sealin the lubricator of the well. At this point, pressure control valvesare closed to isolate the downhole well pressure from the lubricator.Then the pressure within the lubricator can be bled off and thelubricator can be opened to retrieve the tool. However, there can beother reasons why the user identifies tension in the line and,therefore, a misapprehension as to the location of the tool. If the toolis not actually located at or near the uppermost pack-off seal when thepressure control valves are closed the tool can be damaged and/or theline can be cut and the tool can be disconnected from the line andpossibly lost down the well.

SUMMARY

The present disclosure provides a system, an apparatus and a method fordetecting line-attached tools in an above-surface portion of a well foruse during well-work overs and/or interventions.

Some embodiments of the present disclosure relate to an apparatus fordetecting a line-attached tool that is moving through a well. Theapparatus comprises: a body for housing at least one magnetic-fieldgenerator and at least one magnetic-field sensor; and a tubular portionis configured to be housed within the body. The tubular portion has abore for receiving the line-attached tools and the sensor is configuredfor detecting at least one dimension of the line-attached tool whileapproaching, moving through or moving away from the body.

Without being bound by any particular theory, embodiments of the presentdisclosure may provide an operator greater certainty as to the locationof a line-attached tool within an above-surface portion of a well. Thiscertainty may reduce the incidence of false contacts and avoid havingpressure or fluid control mechanisms close directly upon theline-attached tool or close upon and cut the line.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present disclosure will become moreapparent in the following detailed description in which reference ismade to the appended drawings.

FIG. 1 is a schematic of a well with a known line system in place;

FIG. 2 is a schematic of a well with a line system according to oneembodiment of the present disclosure;

FIG. 3 is a schematic of a well with a line system according to anotherembodiment of the present disclosure;

FIG. 4 is an isometric view of an apparatus for detecting line-attachedtools according to an embodiment of the present disclosure: FIG. 4Ashows the apparatus in a closed position with a tubular portionpositioned therein; FIG. 4B shows the apparatus in a partially open anddemagnetized position with the tubular portion positioned therein; andFIG. 4C shows the apparatus in a fully-open position without the tubularportion;

FIG. 5 shows another embodiment of an apparatus for detectingline-attached tools according to an embodiment of the presentdisclosure. for use with the coiled-tubing system of FIG. 1 ; and

FIG. 6 shows one embodiment of the steps of a method for detecting thelocation of a line-attached tool within a well.

FIG. 7 shows a cross-sectional, top plan view of an apparatus fordetecting line-attached tools according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to a system, an apparatusand a method for detecting downhole tools that are attached to a linewhile the tools are being inserted into and/or withdrawn from an oil andgas well. For the purposes of this disclosure, the term “line” refers toany wire or cable that is used to deliver, withdraw and/or operate adownhole tool during a line-facilitated oil-and-gas well operation. Thewires or cables may be slickline or wireline with the understanding thatwireline typically comprises one or more electrical conductors. Someexamples of line-facilitated operations include but are not limited towell completions, well work overs and well interventions. Some examplesof line-attached tools include but are not limited to: a spang, a jar, asinker bar, a perforation gun, running tools, pulling tools, welllogging tools or a bridge plug.

Some embodiments of the present disclosure relate to a system that isinstallable as part of an above-the-surface portion of an oil and gaswell in preparation for, during or after a line-facilitated welloperation. The system comprises a lubricator and a detection apparatus.The system may be incorporated into a Christmas tree of a well and theChristmas tree is fluidly connected with the well head. The Christmastree includes one or more valves for controlling the flow of pressurizedwell-fluids therethrough. The Christmas tree may also include one ormore pressure-containment mechanisms, which are also referred to asblow-out preventer (BOP) systems. BOP systems include members that canbe actuated into and out of a central bore of the Christmas tree tocontain pressurized well-fluids. The lubricator is positioned in fluidcommunication with the well head and above the BOP system.

The detection apparatus generates a magnetic field and detects changesin one or more properties of the magnetic field. For the purposes ofthis disclosure, some of the magnetic-field properties that are detectedand measured by the detection apparatus include but are not limited to:the magnetic flux density of the magnetic field, the polarity of themagnetic field and the amplitude of the magnetic field. The detectedchanges in one or more magnetic-field properties indicate when aline-attached tool is approaching, moving through or moving away fromthe magnetic field within the detection apparatus. In some embodimentsof the present disclosure the detection apparatus can measure one ormore dimensions of the line-attached tool as it moves towards, throughand away from the magnetic field. In some embodiments of the presentdisclosure the detection apparatus can is positioned below thelubricator.

In some embodiments of the present disclosure, the detection apparatuscomprises one or more magnetic-field generators and one or moremagnetic-field sensors. The one or more magnetic-field generatorsgenerate a magnetic field that extends at least partially across acentral passage of the detection apparatus, through which the line andline-attached tool move in and out of the well. The one or moremagnetic-field sensors are electronically connectible to a processor,which in turn provides an output signal that alerts a user that theline-attached tool is approaching, moving through or moving away fromthe detection apparatus. In some embodiments of the present disclosure,the one or more magnetic-field sensors are positioned about the centralaperture of the detection apparatus.

The method comprises a series of steps to identify when theline-attached tool has passed above any valves or pressure-containmentmechanisms while the line-attached tool is moving through theabove-surface-portion of the well. The method comprises a step ofcreating a magnetic field within a section of an oil-and-gas well thatis above the surface. The method also comprises a step of detecting anychanges in the magnetic-field strength that is caused by theline-attached tool approaching, moving through or moving away from themagnetic field. The method may also comprise a step of communicating amagnetic-field strength change signal to a processor wherein theprocessor generates an output signal that alerts a user that theline-attached tool is near or at the section of the well that is exposedto the magnetic field. In some embodiments, the processor is alsoconfigured to determine one or more dimensions of the line-attached tooland to provide that dimensional information within the output signal ora different dimensional output-signal.

FIG. 1 shows a petroleum well 10 from which oil, gas or both may beproduced that extends above and below a surface 76. The well 10 includesan above-surface portion 12 with a well head 16 from whichbelow-the-surface portions 14 of the well 10 extend. The above-surfaceportion 12, which may also be referred to as a Christmas tree, includesa central conduit 17 that can be made up of one or more sections. Eachsection of the central conduit 17 may be connected by flange connections22 and 24. The above-surface portion 12 may also include a lower mastervalve 18 and an upper master valve 20. In some embodiments of thepresent disclosure, above the upper master valve 20 there is a blow-outpreventer (BOP) system 50 that includes at least a lower BOP 52 and anupper BOP 54. The BOPs 52 and 54 may be hydraulically actuated rams orany other type of well-pressure control system. The master valves 18, 20and the BOP system 50 are part of the well's 10 pressure containmentsystem. A lubricator 28 is positioned above the BOP system 50. Thelubricator 28 may include a tool trap 26 and a wireline pack-off 30.Some embodiments of the present disclosure relate to a BOP system 50that includes only one of the lower BOP 52 or the upper BOP 54 and/oronly one of the master valves 18, 20.

FIG. 1 shows a line 32 moving through the top of the lubricator 28 at arotatable shiv 34 from a spool 36. The spool 36 may rotated fordelivering the line 32 into or out of the well 10. Rotation of the spool36 may be controlled by a motor (not shown). The line 32 can be eitherslickline, wireline or other type of well-intervention line. The line 32can extend through the above-surface portion 12 and into thebelow-surface portion 14. Although not shown, it is understood that theline 32 may have one or more of line-attached tools attached thereto.Typically, when a line-attached tool is being pulled out of the well theoperator will apply further tension to the line 32 between the shiv 34and the spool 36. With this further tension, the operator expects todetect when the line-attached tool contacts the lower surface of thewireline pack-off 30. When this occurs, the operator will typicallyclose either or both of the BOPs 52, 54 and/or one or both of the mastervalves 18, With these pressure containment systems closed theline-attached tool can be withdrawn from the lubricator 28 without anuncontrolled flow of pressurized well-fluids, which is also referred toas a blowout. However, often times the operator may detect a falsecontact between the line-attached tool and the wireline pack-off 30.During a false contact the line-attached tool may not be at the top ofthe lubricator 28 but rather lower within the well 10. In some cases,the line-attached tool may be positioned at or below the BOP system 50.If during a false contact one or both of the BOPs 52, 54 are then closedthey may damage the line-attached tool directly and/or the closed BOP52, 54 may cut the line 32 and the line-attached tool may fall down intothe below-surface portion 14 of the well 10. If a portion of the line 32is positioned at either of the master valves 18, 20 when a false contactis detected and the relevant master valve 18, 20 is then closed that mayalso directly damage the line-attached tool or cut the line 32 andresult in the line-attached tool falling down into the below-surfaceportion of the well 10.

FIG. 2 shows another petroleum well 100 that has many of the samefeatures as the well 10 described above. The common features betweenwell 10 and well 100 are shown with the same reference numbers in bothfigures.

The well 100 includes a detection apparatus 102 that is connectiblewithin the above-ground portion of the well 100, 101. The detectionapparatus 102 defines a central passageway 103 that is in fluidcommunication and generally aligned with the central conduit 17. FIG. 2shows the detection apparatus 102 as being positioned within theabove-surface section 12 between the lower master valve 18 and the uppermaster valve 20. FIG. 3 shows another petroleum well 101 that has thesame features as the well 100. The common features between well 100 andwell 101 are shown with the same reference numbers in both figures. Atleast one difference between the well 100 and the well 101 is theposition of the detection apparatus 102. In well 101 the detectionapparatus 102 is positioned above the BOP system but below thelubricator 28. In these arrangements, objects such as the line 32 andany line-attached tools that are moved through the above-surface section12 of the well 100, 101 will also move through the central passage ofthe detection tool 102. The following discussion will describe thedetection apparatus 102 and it is understood that the detectionapparatus 102 may be positioned at different locations within theabove-surface section 12. In some embodiments of the present disclosurethe detection apparatus 102 is positioned below the lubricator 28.

The detection apparatus 102 can generate a magnetic field and detectwhen a line-attached tool approaches, passes through or is moving awayfrom the magnetic field. In some embodiments of the present disclosurethe detection apparatus 102 can also detect and/or measure dimensions ofthe line-attached tool including at least the diameter and length of theline-attached tool.

In some embodiments of the present disclosure the detection apparatus102 is as described in U.S. Pat. No. 9,097,813 and U.S. patentapplication Ser. No. 14/423,090 and the entire disclosures of which areincorporated herein by reference.

In some embodiments of the present disclosure, the detection apparatus102 comprises one or more magnetic-field generators 260, in the form ofone or more magnets, and one or more magnetic-field sensors 270, asshown in FIG. 7 . The one or more magnetic-field generators 260 areconfigured to generate a magnetic field that at least partially extendsinto a central passageway of the detection apparatus through which theline 32 and the line-attached tool pass as they are moved into and outof the well 100, 101.

The one or more magnetic-field generators generate a magnetic field thatpenetrates at least partially across but preferably substantially acrossthe entire central passage of the detection apparatus 102. The magneticfield may be visualised by magnetic field lines that leave the northpole of each magnetic-field generator and return to the south pole ofeach respective magnetic-field generator. Either one of the poles mayface the central passage of the detection apparatus 102. When magneticfield lines return from the north pole to the south pole they penetratethrough the central passage. There are infinite possible return pathsthat the magnetic field lines may utilize to return from north to southpole, and some of those paths pass through one or more of themagnetic-field sensors. The magnetic-field sensors produce an electricalsignal that relates to the strength of the magnetic field passingthrough it. In other words, the electrical output signal from eachmagnetic-field sensor relates to the number of the magnetic field linespassing through each magnetic-field sensor. Some of the return pathshave lower magnetic resistivity that other paths, which causes moremagnetic field lines returning through those paths.

When an object that can perturb or change one or more properties of themagnetic field, such as a section of line 32, a line-attached tool orany other ferromagnetic object approaches, moves through or moves awayfrom the detection apparatus 102 and the magnetic field the objectperturbs or alters the magnetic circuit by changing the magneticresistivity of some of the paths that the field lines travel. Thisperturbation may change the number of the magnetic field lines returningthrough some paths. Some of the altered paths are the paths that passthrough one or more of the magnetic-field sensors, which changes thenumber of the returning magnetic field lines that pass through the oneor more magnetic-field sensors, which in turn causes changes in theoutput from these one or more magnetic-field sensors.

If multiple magnets are used in the detection apparatus 102, the magnetsmay be configured such that the same magnetic pole of each magnet facesthe central passage 103 of the detection apparatus 102. The magnetscreate a magnetic field that corresponds to the magnetic poles facingthe center of the detection apparatus 102. This magnetic field will bestrongest on or near an internal wall 105 of the detection apparatus 102that defines the central passage 103, in front of the magnets, and thestrength of the magnetic field may decrease distally from each magnet.Using multiple magnets may create a substantially homogeneous and evenlydistributed magnetic field that extends at least partially and, in someembodiments, substantially across the central passageway 103 of thedetection apparatus 102.

The magnetic-field sensors are used to detect the strength of themagnetic field. The magnetic-field sensors may be configured to detectchanges in the magnetic field strength proximal or at the center of thedetection apparatus 102. The magnetic-field sensor may be positionedupon a ferromagnetic rod, which can attract the magnetic field towardthe magnetic-field sensors.

This change in one or more properties of the magnetic-field, such as themagnetic-flux density, is detected by the magnetic-field sensors. Whenthe object is closest to a particular magnetic-field sensor near theinternal wall of the detection apparatus 102, most of the magnetic fielddirected towards that particular magnetic-field sensor is drawn towardthe object, which causes that particular magnetic-field sensor to detectless of the magnetic-field strength. As the ferromagnetic object movesaway from the particular magnetic-field sensor, the magnetic fieldstrength detected by the magnetic-field sensor increases drasticallydepending on how far the surface of the ferromagnetic object is. Byobserving the magnetic field strength detected by a particularmagnetic-field sensor, the distance between the surface of theferromagnetic object and the magnetic-field sensor can be determined.

The absolute magnetic field strength read by the magnetic-field sensorsdepends on the strength of the magnets positioned within the detectionapparatus 102. However, changes in the magnetic-field strength withinthe detection apparatus 102 can be due to the presence of aferromagnetic object and the magnitude of those changes can depend onthe dimensions and/or material properties of the ferromagnetic objectand its location within the detection apparatus 102.

When multiple magnets and multiple magnetic-field sensors 270 are used,the diameter and the position of the center of the ferromagnetic objectmay be found by determining the distance between the surface of theferromagnetic object and each magnetic-field sensor.

The detection apparatus 102 can stream the magnetic-field strengthreadings from the different magnetic-field sensors to a processor unitthat converts these readings into ferromagnetic object-to-sensordistances. These distances may then be used to calculate variousdimensions of the ferromagnetic object including at least the diameter,length and the center coordinates. The processor unit can send a visualrepresentation of these calculated dimensions in real-time to anoperator's screen.

The conversion of the magnetic-field strength reading to a distance isdone by comparing the magnetic-field strength readings to knownmagnetic-reading curves that were obtained under known conditions andknown distances for known sizes of ferromagnetic objects. To convert thedistances obtained from different magnetic-field sensors within thedetection apparatus 102 to position and diameter information, theprocessor unit may use the Apollonius theory and/or the circle equationmay be used.

For example, one embodiment of the detection apparatus 102 includes afirst sensor array that includes one or more sensor units and one ormore magnets. Some embodiments of the detection apparatus 102 includemultiple sensor arrays. Within the first sensor array, the sensor unitsand the magnets are arranged in an alternating pattern, but thisalternating pattern is not required.

The sensor array may comprise a body with a plurality of sensor borestherein each adapted to receive an individual sensor unit therein. Insome embodiments of the present disclosure, the sensor unit comprises asleeve and a sensor. The body may be an annular or ring-shaped spoolhaving the inner surface and an outer surface that extend between a topsurface and a bottom surface. The inner and outer surfaces aresubstantially cylindrical about a central passage. When the detectionapparatus 102 is integrated into the well 100, 101, the central passagemay be co-axial with a central passage of the other components of theabove-surface portion 12 of the well 100, 101. The inner surface definesa central passage that extends therethrough, which may be sized andshaped to receive the line 32 and any line-attached tools, which can beof various dimensions and sizes. In some embodiments of the presentdisclosure, the top surface and the bottom surface may be substantiallyplanar along a plane normal to the central passage. Optionally either orboth of the top surface and the bottom surface may include a seal groovethat extends annularly therearound for receiving a seal, as is known inthe art.

Other embodiments of the present disclosure comprise a detectionapparatus 102A as shown in FIG. 4A, FIG. 4B and FIG. 4C. The detectionapparatus 102A has the same functions and many of the same components asthe detection apparatus 102 described above. Furthermore, the detectionapparatus 102A may be similarly positioned within theabove-surface-portion 12 as the detection apparatus 102.

As shown in FIG. 4A the detection apparatus 102A comprises a body 200and a tubular portion 202 that is positionable within the body 200. Thebody 200 can be configured to retain the tubular portion 202. The body200 can move between a closed position (as shown in FIG. 4A), apartially-open position (as shown in FIG. 4B) and a fully-openedposition (as shown in FIG. 4C). In some embodiments of the presentdisclosure the body 200 may comprise a first body 204 and a second body206. The first body 204 comprises one or more magnetic-field generatorsand one or more magnetic-field sensors that can be housed within bores(not shown) of the first body 204. Each bore may be covered with a borecap 208. The bore caps 208 can ensure that the magnetic-field generatorsand the magnetic-field sensors are contained within their respectivebores. The magnetic-field generators can be magnets that create amagnetic field proximal to the first body 204. Some examples of themagnets include but are not limited to: one or more rare earth magnets,one or more magnetized ferromagnetic bodies or one or moreelectromagnets. The magnetic-field sensors can detect perturbations inthe magnetic field and/or the magnetic flux proximal the first body. Themagnetic-field sensors are electronically connectible to the processorunit (not shown) to generate a processor output that identifies when aline-attached tool is approaching, moving through or move away from themagnetic field. The magnetic-field sensors can also detect at least onedimension of the line-attached tool that is perturbing the magneticfield including one or more of the cross-sectional diameter, length andprofile and this dimensional information can also be included in theprocessor output.

The first body 204 can include an actuating member (not shown) thatallows the first body 204 to move between a closed position (as shown inFIG. 4A) and an open position (as shown in FIG. 4B and FIG. 4C). Forexample, the actuating member may be a hinge and the body 204 may be aclam-shell type of arrangement. The first body 204 may also include oneor more connectors 210 that can hold the first body 204 in the closedposition. While FIG. 4A shows the connector 210 as a pin and slotarrangement, other types of connectors 210 are contemplated.

The second body 206 may comprise an upper second body 206A that ispositioned above the first body 204 and a lower second body 206B that ispositioned below the first body 204. The upper bodies 206A, 206B canalso move between a closed position (as shown in FIG. 4A and FIG. 4B)and an open position (as shown in FIG. 4C). When the first body 204 andthe second body 206 are both open, the body 200 is in the fully-openedposition. The second bodies 206A, 206B may also include actuatingmembers and connectors 212 that allow the second bodies 206A, 206B tomove between the open and closed positions and to hold the second bodies206A, 206B in the closed position, respectively.

In some embodiments of the present disclosure, the tubular portion isconfigured to be housed within the body 200. The tubular portion 202 canhave a central bore 214 through which the line 32 and any line-attachedtools may be received and pass therethrough. The tubular portion 202 maybe made of a non-ferromagnetic material, metal or alloy that comprisesone of nickel, chromium, iron or combinations thereof. One non-limitingexample of such a non-ferromagnetic material is INCONEL® (INCONEL is aregistered trade-mark of Vale Canada Limited).

In some embodiments of the present disclosure the one or more magneticfield generators may be electromagnets and when the first body 204 ofthe body 200 is in the closed position, the magnetic field generatorsmay be activated and the magnetic field is generated. When the firstbody 204 is in the open position the magnetic field generators are off.

In some embodiments of the present disclosure, the body 200 may compriseone or more sections that can be connected together to form a completebody 200 that is held together by multiple connectors 212. In theseembodiments the body 200 does not include an actuating member.

FIG. 5 shows another example of a detection apparatus 400 that has manyof the same components as the detection apparatus 102 described hereinabove. Components that are the same between the different detectionapparatus 102 and 400 are referred to in FIG. 5 using the same referencenumbers as used in the other figures herein. The detection apparatus 400shown in FIG. 5 is similar to the apparatus described in the applicant'sprior patent application WO 2017/205955 entitled APPARATUS AND METHODFOR MEASURING A PIPE WITHIN AN OIL WELL STRUCTURE, the entire disclosureof which is incorporated herein by reference. Briefly, the detectionapparatus 400 comprises a tubular body 402 that defines a centralpassage between first and second ends. The tubular body 402 has at leastan outer surface that is formed of a non-magnetic material. In someembodiments of the present disclosure, some or all of the tubular body402 is formed of a non-magnetic material. Each of the first and secondends has a flange 404 that extends outwardly therefrom, substantiallyperpendicular to the central passage. The flanges are connectible withother components of the well 100 so that the central passage issubstantially aligned with the central conduit 17 of the well 100. Thedetection apparatus 400 may include multiple magnetic-field generators260 and multiple magnetic-field sensors 270 that are arranged in one ormore arrays 201, as described herein above. The arrays 201 may bepositionable around the tubular body 402 upon the outer surface. Thearrays 201 may operate in the same manner as described herein above todetect changes in one or more properties of the magnetic field asferromagnetic objects approach, move through or move away from thedetection apparatus 400.

Some embodiments of the present disclosure relate to a method 500 fordetecting the location of a line-attached tool during a well lineoperation (see FIG. 6 ). The method comprises the step of creating 502 amagnetic field within at least a portion of an above-surface-portion ofthe well. The method includes a step of detecting 504 one or moreproperties of the magnetic field. The step of detecting 504 may alsoinclude a step of detecting a change in the one or more properties ofthe magnetic field that are caused by the line-attached toolapproaching, moving through or moving away from the magnetic field. Themethod further includes a step of communicating 506 an output signal toa processor that indicates the one or more detected properties and/orthe detected change in the one or more detected properties of themagnetic field. In some embodiments of the present disclosure, theprocessor is configured to determine the location of the line-attachedtool within or near to the magnetic field. The method may also includean optional step of generating 508 an output signal that alerts a userthat the line-attached tool is near or at the above-surface-portion ofthe well proximal the magnetic field.

I claim:
 1. An apparatus for detecting a line-attached tool that ismoving through a well, the apparatus comprising: (a) a body that definesa central passageway for receiving the line-attached tool therethrough;(b) at least one magnetic-field generator that is configured to generatea magnetic field that extends at least partially across the centralpassageway; and (c) at least one magnetic-field sensor that isconfigured for detecting a change in one or more properties of themagnetic field that are caused by the line-attached tool approaching,moving through or moving away from the magnetic field.
 2. The apparatusof claim 1, wherein the at least one magnetic-field generator is housedwithin the body.
 3. The apparatus of claim 1, wherein the at least onemagnetic-field sensor is housed within the body.
 4. The apparatus ofclaim 1, wherein the body is connectible with well in an arrangementwhere the central passage is substantially aligned with a central boreof the well.
 5. The apparatus of claim 1, wherein the body isconnectible to the well below a lubricator of the well.
 6. A method foridentifying a location of a line-attached tool while moving through anabove-surface-portion of a well, the method comprising steps of: (a)creating a magnetic field within at least a portion of theabove-surface-portion of the well; (b) detecting changes in one or moreproperties of the magnetic field that are caused by the line-attachedtool approaching, moving through or moving away from the magnetic field;(c) communicating an output signal to a processor that indicates achange in the one or more detected properties of the magnetic field,wherein the processor is configured to determine the location of theline-attached tool within or near to the magnetic field; and (d)generating an output signal that alerts a user that the line-attachedtool is near or at the above-surface-portion of the well proximal themagnetic field.
 7. The method of claim 6, wherein the processor is alsoconfigured to determine one or more dimensions of the line-attachedtool.